It is known to manufacture low pressure drop (LPD) turbulizers by stamping metal strip stock to form it with transverse corrugations having openings and offset portions formed in side walls of the corrugations. In known stamping processes, a single transverse corrugation is created by each stamp cycle. Accordingly, this process is relatively slow and expensive. Further, as there are practical limits in terms of the amount by which the material can be deformed during stamping without fracture, turbulizers produced by this method typically have a relatively low ratio of corrugation amplitude to pitch and relatively low offset distance. However, known transverse-stamping processes of this type are nonetheless widely used, as same permit the manufacture of turbulizers of high utility, flowing from the geometry of the corrugations, openings and offsets obtainable. Of note, a turbulizer can be produced by this methodology which has substantially vertical corrugation sidewalls, i.e. sidewalls orientated normally to the plane of the turbulizer. Such a turbulizer, suitably brazed inside a flat tube, can render the tube relatively resistant to deformation, even under relatively high pressures. As well, balanced turbulizers can be produced by this method, i.e. turbulizers wherein the “blades” of the turbulizer (the planar portions of the turbulizers orientated parallel to the flow) are substantially equally spaced from one another.
It is also known to form LPD turbulizers by rolling or stamping strip stock to form a longitudinally-corrugated strip of sinusoidal profile, and, as indicated schematically in FIG. 1, to pass the longitudinally-corrugated strip 2 through a stamping press 5 wherein upper 6 and lower 7 dies are brought to bear against same to transversely/laterally cut and displace the corrugations to form a material 3 having corrugations having openings and offset portions formed in sidewalls of the corrugations. This process, described in United States Patent Application Publication No. US2005/0016240, published Jan. 27, 2005, which publication is hereby incorporated by reference, is relatively fast and inexpensive, but turbulizers of sinusoidal profile are not always desired since they can be difficult to produce in balanced form and do not provide the same burst strength as turbulizers with vertical corrugation sidewalls.